Head-mounted display devices (also called herein head-mounted displays) are gaining popularity as means for providing visual information to a user. For example, head-mounted display devices are used for virtual reality and augmented reality operations.
When operating head mounted displays, it can be desirable to track an eye of a user in order to direct images toward the user's eyes. In most cases, eye-tracking requires an illumination source to provide light for illuminating the eye and a camera or detector to receive light reflected off the eye. The placement of the illumination source and camera may be challenging since the components required for eye-tracking need to be located so that they do not obstruct a user's view of the display as well as be able to sufficiently illuminate the eye and receive light reflected at the eye.